The present invention relates to the steering of motor vehicles and, in particular, to the steering of motor vehicles where both the front wheels and rear wheels are steerable.
In most conventional vehicles, steering is accomplished using only the front wheels. However, having the rear wheels also steer increases maneuverability and has been used in cars, riding lawn mowers, and special-purpose vehicles. Control has been realized by linking front and rear steering to be operated with a single steering wheel or by using two independent systems controlled separately, either by two controls—as in a long fire truck with a second driver in the rear to drive the rear end—or with a switched control. However, linked controls, in which both front and rear wheel systems work together to give a shorter turning radius, do not allow a sideways or crabbing movement, such as might be used in changing lanes or in parallel parking. To exploit the full advantages of independent front and rear steering systems giving both tight turns and crabbing under the control of the driver requires two degrees of freedom: one for the front and one for the rear set of wheels. Two steering wheels could provide this, but would require two hands and would fail to allow the driver to respond with a quick “instinctive” response. Indeed, such a system could be dangerous, except at slow speeds.
The present invention is directed to a new and improved motor vehicle steering control which provides two degrees of freedom to steer both the front wheels and rear wheels of a vehicle, but which requires only one hand to use.